1. Field of the Invention
The invention relates to a process and apparatus for truncating tubes and more particularly, but not exclusively, tubes made of cardboard or plastic.
2. Discussion of Background and Material Information
The truncation of tubes made of cardboard or other materials is conventionally accomplished by means of a saw or with one or more knives. Typically a knife-blade arrangement is preferred for materials which are not too hard because knives normally result with cleaner cuts.
Tubes of this type are generally rotated on a mandrel adjacent at least one knife which is activated by a jack adapted to bring the knife towards the tube and to cause the blade of the knife to penetrate into the wall of the tube. Generally, the knife cuts entirely through the wall of the tube until it meets a counter portion, stop, or a harder counter knife at which point the direction of the knife is reversed. The counter can, for example, be formed by the mandrel itself or be separately provided as an attachment to a portion thereof. As one would expect, the counter or hard surface against which the knife contacts causes wear of the knife blade which eventually becomes dull.
In order to overcome this disadvantage, the present invention has attempted to reduce the pressure exerted by the knife at the moment when the knife comes into contact with the counter. As one will appreciate, it is very difficult to accurately adjust a jack or other hydraulic or pneumatic device to exert an appropriate and precise pressure on the knife in the course of the cut so as to reduce the pressure or force exerted on the knife at the end of the cut when the blade is about to contact the counter. The novel and unique apparatus of the present invention, however, effectively overcomes these disadvantages by interrupting the force initially applied to the knife, for example by a jack or similar mechanical, hydraulic or pneumatic device, as the knife cuts into but before the blade penetrates through the tube, while activating a means for exerting supplemental pressure on the knife, which is less than the force initially applied by the knife, until the cut is complete.